US2682337A - Froth flotation of phosphate values involving ph control - Google Patents

Description

June 29, 1954 w. A. HODGES ETAL 2,682,337

FROTH FLOTATION OF PHOSPHATE VALUES INVOLVING PH CONTROL Filed Dec. 29, 1950 zz/q Josepk E F/ogd Patented June 29, 1954 FRO'ILH FLOTATION 0F PHOSPHATE VALUES INVOER/HN@ pH CONTROL William A. Hodges, Plant City, and Joseph E. Floyd, Fort Meade, Fla., assignors to Swift & Company, Chicago, Ill., a corporation of Illinois Application December 29, 1950, Serial No. 203,454

2 Claims. (Cl. 209-166) The present invention relates generally to a process for concentrating phosphate ore by selective flotation separation, and more particularly to a process for concentrating phosphate ore wherein pH control is employed to produce a high grade phosphate concentrate.

Phosphate ores have been concentrated by several general methods, the most practical of which comprises treating the ore with reagents adapted to selectively iioat the phosphate particles of the ore upon suitable agitation.

The principal object of the present invention is to provide an improved process for the selective otation of phosphatic material wherein greater yields are obtained.

A further object of the present invention is to provide a process for phosphate flotation involving pH control of the flotation conditions.

Additional objects if not specifically set forth herein will be readily apparent to one skilled in the art from the following detailed description of the invention.

In the drawings:

Fig. l represents a flow sheet for the method of the present invention, showing in diagrammatical form the steps followed in carrying out the invention.

The present invention, in general, comprises the steps oi preconditioning deslilned phosphatic feed, subjecting the conditioned feed to a frothflotation operation, repulping the froth so obtained and refloating to recover a high grade phosphate concentrate.

More specifically, it has been found that if the pI-I values in the various steps are controlled within certain specific limits, the recovery of phoshate is markedly increased. These critical pl-l limits in thD various steps are as follows:

In the pre-conditioning cells, 8.5-9.0 pli;

in the flota-dion cells (initial), 7.8-8.2 pH; and

In the reflotation cells (nal) 6.4-6.8 pl-I.

For example, the phosphatic feed, deslimed by decantation or any conventional method, is first conditioned at approximately 70 per cent solids for about 2 minutes. In carrying out this step, the deslimed feed together with sufficient water to make a pulp of about 70 per cent solids content is introduced into a mister, horizontal or vertical, together with an alkali, fatty acid, and an unsaponiiiable oil, which are added in sufficient quantities as to cause a selective coating ci the phosphate particles. The pH of the conditioning cells is maintained, by correct proportioning oi' the alkali added, within the range 8.6-9.0. The conditioned feed is then passed to i.'

a bank of flotation cells maintained at a pH oi 7.8-8.2, where it is agitated and aerated to produce a froth. This froth, which contains a fairly high percentage of phosphate together with some silica, is then repulped with water and refloated, without using further reagents, in the second bank of flotation cells maintained at a pH of 5.4-6.8. The middlings obtained in this second bank of cells be returned to the conditioning cells to be reworked with new feed ior the purpose of recovering additional B. P. L. values. The froth removed from the second bank of flotation cells will be found to have, as a general rule, about 90 per cent or better of the B. P. l... present in the original feed.

Referring now to the drawing of Fig. l, the deslimed phosphatic feed from a classifier it is passed into a suitable mixer or conditioning cell l i wherein it is throughly mixed and conditioned with water fed into the mixer through line I2 and an alkali-fatty acid-unsaponifiable oil mixture fed in through line I3. The amount of alkali added is regulated so as to maintain a pH of 8.6-9.0 in the conditioning cell. After about 2 minutes from the time that the reagents are added, the conditioned pulp is introduced through line it together with water from line l5 into a dotation machine or bank of rougher cells le. In these cells the pulp is aerated and agitated causing air bubbles to attach to groups of phosphatic particles. These aerated phosphate groups rise to the surface where they are removed as a froth and introduced into a second bank of flotation cells known as cleaner cells il through line It. The siliceous gangue or tailings pass out of the bottom of the rougher cells to waste through line l5). The pl-l of the rougher cells is maintained at '7.8-8.2 by the addition of water of the necessary pH through line l5. In the cleaner cells the phosphate concentrate in the froth from the rougher cells is reoated by the addition of water through lines 20 and again aerated and agitated in the same manner as in the rougher cells. The pH of the cleaner cells is held at 6.4-6.8 by the addition through line 20 of the necessary quantity of acid, prei- Verably sulfuric acid. This operation causes some of the siliceous particles entrapped in the initial otation froth from cells iii to be released and sink to the bottom of the cells Il whence they are removed together with a small amount of phosphatic particles as middlings through line 2i. Those middlings can be recirculated through the entire flotation process as indicated in Fig. 1 to recover additional phosphate values.

The enriched froth obtained in the refloating process in cells il' is removed by paddles and is pumped directly to storage through line t2. The lower pli oi' acts as a depressing agent for the entrapped silica particles and also causes the phosphate particles to be floated more or less as individual particles which is not the case in the initial flotation stage or rougher cells wherein a higher pli. is maintained.

The following specic examples are included for the purpose of illustration only, and are not to be construed as limitations on the invention claimed herein:

Example I For the purpose of illustration, in this and following examples, the conditioning cells will be referred to as the conditioner cell; the first flotation cell as the rougher cell and the second flotation cell as the cleaner cell.

A B (pH of (pH of cleaner cleaner cell, 7.9) cell, 6.5)

pH of conditioner cell 8. 9 9.0 pH ci' rougher cell 8.0 7.8 Pounds reagent/ton feed:

NaOH 0. 30 0.30 Fatty Acid.. 0. 43 0.43 ucl O' 1. 29 1. 29 conditioning time (rn 2 2 time in rougher cell (sec 32 32 time in cleaner' cell (sec.) 34 37 Percent concentrates 39, 4 33.6 3. 1 8.8 57. 5 57.6 31. 49 31.09 73. 63 76.69 15. 35 42.99 3. 49 2. 6l 5. 62 3. 00 o\ ed rougher cell., 93. 62 95. 16 Percent B. P. L. recovered in final product. 92. 12 82. 98 Percent B. P. L. recovered by reworklng middlings 93. 51 93.05 Percent SiO in rougher concentrate eliminated in cleaner cell 52.2 79. 5

Example II In the following example, the pH of the cleaner cell under A was held at '7.6; and the pH of the cleaner cell under B was held at 6.6.

(Middlings could be reworked to recover additional B. P. L. values.

Example III Under A, cleaner cell pH was held at 7.8.

Under B, cleaner cell pH was held at 6.6. Under 0, cleaner cell pH was held at 6.4.

A B C pH of conditioner cell...

pH of rougher cell Pounds reagents/ton fee Percent concentrates... Percent middlmgs Percent tailmgs..

B. P. L. Tailings..- SiO Concentrates Percent B. P. L. in Feed l0 Percent B. P. L. in Concentrates... Percent B. P. L. in Middlings Percent B. P. L. in Tailings Time in rougher cell (see.) 3 Time in cleaner cell (sec.) 3

The above examples illustrate that a higher B. P. L. content is found in the recovered phosphate when the pH of the cleaner cell is lowered. This results in a somewhat higher percentage of middlings, which however may be reworked to recover additional B. P. L. values. The pH values for the conditioning, flotation, and reflotation steps are critical and must be carefully maintained in order to obtain the increased recovery of phosphate values made possible by the present invention. In the conditioning and initial flotation steps a higher pH than the range specied results in a large quantity of foam formation with attendant flotation of undesirable silica. In these steps a pH below the specified range results in a depressing action which causes the excessive loss of phosphate values in the tailings. In the cleaner cells or reilotation step, a pH above the critical range specified results in a lower grade of recovered phosphate concentrates, while a lower pH than specified results in prohibitive loss of phosphate values in the middlings.

The particular collecting agent does not form part of the present invention and any suitable agents may be substituted for the fatty acid-fuel oil-NaOH mixture illustrated herein. For example, instead of NaOH, the alkali used may be potassium hydroxide, ammonium hydroxide, anhydrous ammonia, and less preferably, the hydroxides of calcium, barium, and lithium. Oleic and linoleic acids are the best fatty acid reagents, but other unsaturated fatty acids can be used successfully. All fatty oil acids such as cottonseed, palm, peanut, soyabean, sh, tall oil, etc., can be used. Also, soaps made from these fatty acids and sulphonated fatty acids and sulphonated petroleums can be used. Fuel oil having a gravity of 20 Baum is preferred, although lighter or heavier petroleum oils can be used. Unsaponifable fatty oils can also be used.

The term deslimed phosphatic feed as used in the appended claims is intended to cover a mixture of deslimed ore and water forming a pulp of suitable consistency for handling in the conditioning cells, preferably as aforesaid comprising about a 70 per cent solids content.

Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A process for the froth flotation of phosphate values from deslimed phosphatic ore which comprises: intimately mixing with deslimed phosphatic feed a mixture of reagents comprising an alkali, a fatty acid and an unsaponiable oil at a pH within the range of 8.6-9.0; passing the resulting mixture of deslimed feed and reagents into an agitating zone maintained at a pH within the range of '7.8-8.2 whereby a phosphate-bearing froth is formed; repulping said froth with water and refrothing at a pH within the range of 6.4-6.8 to produce a froth containing substantially all recoverable phosphate.

2. A process for the froth-flotation of phosphate values from deslimed phosphatic ore which comprises: conditioning deslimed phosphatic feed with a mixture of an alkali, a fatty acid and an unsaponiable oil at a pH of from 8.6-9.0; frothing the resulting mixture in an agitating zone at a pI-I of from 7.8-8.2 to form a phosphatebearing froth; separating out the froth so formed and repulping at a pH Within the range of 6.4-6.8; and refrothing the mixture at this pH to oat substantially al1 recoverable phosphate in the form of a high phosphate-content concentrate.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,293,640 Crago Aug. 18, 1942 2,461,813 Duke Feb. 15, 1949 Number Milling 6 FOREIGN PATENTS Country Date Great Britain Apr. 22, 1941 Great Britain Dec. 20, 1948 OTHER REFERENCES Methods for 1934, published by the A. I. M. M. E., New York, N. Y., 1935, pages 452 and 460. 0

(Copy in Div. 25.)

Claims (1)

1. A PROCESS FOR THE FROTH FLOTATION OF PHOSPHATE VALUES FROM DESLIMED PHOSPHATIC ORE WHICH COMPRISIES: INTIMATELY MIXING WITH DESLIMED PHOSPHATIC FEED TO A MIXTURE OF REAGENTS COMPRISING AN ALKALI, A FATTY ACID AND AN UNSAPONIFIABLE OIL AT A PH WITHIN THE RANGE OF 8.6-9.0; PASSING THE RESULTING MIXTURE OF DESLIMED FEED AND REAGENTS INTO AN AGITATING ZONE MAINTAINED AT A PH WITHIN THE RANGE OF 7.8-8.2 WHEREBY A PHOSPHATE-BEARING FROTH IS FORMED; REPULPING SAID FROTH WITH WATER AND REFROTHING AT A PH WITHIN THE RANGE OF 6.4-6.8 TO PRODUCE A FROTH CONTAINING SUBSTANTIALLY ALL RECOVERABLE PHOSPHATE.

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